As the projection-type display device, there is a projector for magnifying and displaying an image or a video. The projector is widely used for a personal theater, business presentation, and the like. The projection-type display device includes a light source, an optical engine having an optical system that acts on light emitted from the light source, and a heat dissipation mechanism for dissipating heat from the light source.
For the light source of the projection-type display device, an ultrahigh pressure mercury lamp is frequently used. However, the ultrahigh pressure mercury lamp has problems that include a short life and environmental pollution that is caused by mercury. An optical system is necessary for separating white light into lights of three primary colors, and etendue is large. Consequently, it is difficult to design a compact device.
Recently, development has been pursued on a projection-type display device which uses, as a light source device, a light emitting element such as a laser diode (LD) or a light emitting diode (LED). Such a light emitting element has the advantages of consuming a low amount of power and long life. The light emitting element emits light and generates heat. In such a light emitting element, a part of electric current applied to generate light is converted into Joule heat, and accordingly the light emitting element itself generates heat. For example, in the case of a light emitting element where light-power conversion efficiency (Wall-Plug Efficiency: WPE) is 30%, 30% of applied power is used for light generation, and the remaining 70% is converted into heat in the light emitting element.
The characteristics of the light emitting element depend on temperature. The increase of the temperature of the light emitting element affects the wavelength of light, the optical output, or the element life. In Particular, in the case of the LD, an oscillation wavelength usually shifts to a long wavelength side when the temperature increases, or the efficiency of converting electric current into a light output, namely, slope efficiency, declines. This necessitates stable dissipation of heat from the light emitting element and members in the vicinity during the operation of the light emitting element.
JP 2006-147744 A discloses a light source device which includes a light emitting element such as an LD or an LED, a substrate for supporting the light emitting element, and a plurality of heat dissipation fins of a heat sink. The fins extend toward the rear surface of the light emitting element. The light source device further includes a fan for blowing air to the plurality of heat dissipation fins. Heat generated in the light emitting element is dissipated by air that blows from the fan to the plurality of dissipation fins.
In the case of a compact and thin light source device, the area of a region where heat dissipation fins are formed is limited, and thus it is difficult to secure sufficient heat dissipation performance. When the area of the region where the heat dissipation fins are formed is increased to secure sufficient heat dissipation performance, the light source device is enlarged.
In the light emitting element such as an LD or an LED, an electric terminal for supplying power to the light emitting element extends in a direction opposite the emitting direction of light. This electric terminal is generally connected to a circuit formed on a wiring board, and is electrically connected to a driver via the wiring board. The arrangement of the wiring board behind the light emitting element may limit the area where the heat dissipation fins are formed. In particular, in the case of the high-output LD, large electric current must be applied, and thick wires must be laid, thus increasing the size of the wiring board. Thus, the installation area of the heat dissipation fins is smaller, and it may even be difficult to install heat dissipation fins. As a result, the heat dissipation effect of the light emitting element declines. If the amount of air that is blown by the fan is increased to compensate for the shortage of heat dissipation performance, noise will increase.
JP 2010-197497 A discloses a projector which includes a laser emitting device as an excitation light source for applying excitation light, a phosphor irradiated with the excitation light to emit light, and a cooling fan. The cooling fan is disposed on the downstream side of the laser emitting direction of the laser emitting device. An exhaust noise reduction device is disposed on a side opposite the cooling fan sandwiching the laser emitting device. Accordingly, air that is sent out from the cooling fan may advance linearly alongside the laser emitting device to reach the exhaust noise reduction device.
Thus, in a cooling method where the cooling air is caused to advance linearly alongside a heat generator such as a light emitting device, an increase in the wind velocity of the cooling air is accompanied by an increase in cooling efficiency. However, when a large cooling fan is used to sufficiently increase the wind velocity of air, this causes an increase in the size of the projector, and noise increases. When miniaturization of the cooling fan and reduction of noise are tried, sufficient wind velocity cannot be set, nor is the heat dissipation effect of the light emitting element adequate.
Thus, there is a demand for a light source device small in size and low in noise, and having a heat dissipation mechanism capable of effectively dissipating heat from a light emitting element such as an LD or an LED, and a projection-type display device including the same.